1. Field of the Invention
The present invention relates to a structure of a zoom lens barrel capable of executing focusing.
2. Related Art Stament
Image-pickup apparatuses such as a camera, an electronic camera, and the like have a lens barrel for holding an image pickup lens. In particular, when the image pickup lens is a lens capable of executing zooming, the lens barrel is called a zoom lens barrel.
An image pickup lens held by the zoom lens barrel is generally divided into a plurality of lens groups such as a lens group for mainly executing focusing, a lens group for mainly executing zooming, and the like depending on the optical functions born thereby. More specifically, there is an example in which a lens group (first group lens) disposed nearest to an object is called a focus lens group, a lens group (second group lens) disposed on the second nearest to the object side is called a zoom lens group. There is known a floating lens arranged to correct spherical aberration and the like by further dividing the focus lens group into a front group and a rear group and relatively moving the front group and the rear group according to an object distance.
As an example of a conventionally proposed zoom lens barrel having the above arrangement, there is exemplified a zoom lens barrel in which both a first group lens and a second group lens are moved in an optical axis direction and about an optical axis in both zooming and focusing.
A zoom lens barrel proposed in Japanese Unexamined Patent Application Publication No. 4-52628 relates to a lens barrel having a fixed frame and a movable lens holding frame and executing zooming or focusing by rotating the lens holding frame or moving it forward and rearward. In more detail, in the zoom lens barrel, a focal distance is changed by rotating or forward and rearward moving a first lens holding frame and a second lens holding frame and further a focusing operation is executed by moving the second lens holding frame forward and rearward, resulting in shortening the overall length of the lens barrel.
Further, in recent years, a great number of the zoom lens barrels described above are optically arranged to include an aspherical lens in addition to a spherical lens to obtain a higher optical performance.
Further, a lens hood is conventionally attached to the distal end of the zoom lens barrel. The lens hood prevents occurrence of flare and ghost by cutting light incident from the outside of an image pickup range. When the lens hood is a type attached to a lens barrel having a telescopic side focal distance, the lens hood often has such a structure that a conical surface is combined with a cylindrical surface. However, when the lens hood is a type attached to a lens barrel having a wide angle side focal distance, a lens hood cut in a complex shape is used so that an image to be picked up is not vignetted by it. In more detail, the lens hood having the complex shape is formed in a shape for cutting light outside of a rectangular image pickup range in a circular image circle formed by an image pickup lens. Accordingly, although the lens hood is formed symmetrically up and down and right and left, the lens hood is not suitably used when it is rotated in, for example, an oblique direction.